Graphical user interfaces have become a standard for interfacing between a user and a computer. Such interfaces are in wide use in computer operating system interfaces produced by Apple, Microsoft and others. These interfaces are limited in that they are intended for interfacing between a user and a computer having a two dimensional display such as a CRT or LCD. A user activates the interface with a key board and or a pointing device such as a mouse pointing to an icon on the display. Advancements have been made with the advent of a touch screen which allows a user to approximately contact the icon or intended area of the graphical user interface in order to use the interface. However, contact with the touch screen can contaminate the display area of the screen with finger prints and other types of smudges. Also, constant physical contact with the touch screen can result in its mechanical failure. Thus, what is needed is a way to contact user interface images without contacting a keyboard or a mouse or the display itself.
Three dimensional image displays are improving. Several types of three dimensional displays are known including stereoscopic displays which display a virtual three dimensional image using filters to highlight images intended for each eye of the viewer, thereby providing a stereoscopic or three dimensional affect. Such systems alternately flash images for the left and right eye of the user and require a filter for each eye, usually included in glasses worn by the viewer. Systems are in public use which require glasses may have color filters, orthogonally polarized lenses, or actively switched lenses, and the display is correspondingly modulated with left and right eye images to provide the three dimensional effect. Furthermore, stereoscopic displays which do not require glasses have been described, descriptions are included in U.S. Pat. No. 4,987,487, Jan. 22, 1991, to Ichinose et al. entitled Method of stereoscopic images display which compensates electronically for viewer head movement, and U.S. Pat. No. 5,365,370, Nov. 15, 1994, to Hudgins entitled Three dimensional viewing illusion with 2D display. Yet another stereoscopic display system in completely contained in a head set worn apparatus as described in U.S. Pat. No. 5,673,151 Sep. 30, 1997 to Dennis entitled Image correction in a virtual reality and heads up display. The aforesaid patents are incorporated by reference. The aforesaid stereoscopic displays allow the viewer to simultaneously observe both a stereoscopic object, appearing to be generally set apart in three dimensions from the image projection means, and a physical object, such as the hand of the user, in approximately the same perceived space. What is needed is a method and apparatus by which the intersection of the physical object and the stereoscopic object can form a user interface with a computer system.